Selecting multipurpose trees

This module provides
basic guidelines on how to select species of multipurpose trees that
will meet farmers' particular needs. The importance of matching tree
species with the characteristics of the site where they will be
grown is stressed. The module also outlines the possible advantages
of growing trees, whether it be for domestic purposes or for
generating income.

What is a multipurpose tree?

Farmers have been growing
trees for different purposes for thousands of years. Certainly, all
trees provide shade and protection from soil erosion. In this sense, all
trees can be said to have at least two purposes. More precisely, though,
this manual uses the term multipurpose tree species to mean:

tree species that are grown
to provide more than one significant crop of function or form. These may
include soil conservation, shade, fuelwood, timber, fibre, fodder, food
or medicine.

Tree species can be multipurpose in two ways:

A single tree can
yield more than one crop. For example, farmers in Central
America and the Philippines grow Gliricidia sepium as living fences
that provide fuel, fodder, and green manure for agricultural crops —
all at the same time.

Trees of the same
species, when managed differently, can yield different crops. In
the Philippines, for example, Leucaena leucocephala is
managed so that some trees will principally yield wood while others
principally produce leaf meal.

Farmers can grow
multipurpose trees in various combinations with other crops, as in
agroforestry, in block plantations of trees or in naturally
regenerating tree farms.

In certain settings, multipurpose trees are
grown and managed for only one purpose. In the Solomon Islands,
Gliricida sepium is grown only to provide shade in coffee
plantations. The same species is planted in Central America and the
Philippines, yet the way it is managed results in a very different
shape and use.

Farmers facing changing conditions in their
environment or market can also change the way they manage a tree.
For example, market changes may persuade farmers, who previously
grew trees for fodder and fuel, to cut their trees for sale as
roundwood for construction material.

Why grow multipurpose trees?

Reducing risk of total
crop failure

Growing multurpose trees
can reduce the risk of total crop failure. For example, if farmers
usually grow Leucaena leucocephala for animal fodder and the
tree's leaves are destroyed by pests, they will still have wood that
can be used for fuel, pulp, or light-weight construction material.

Having a variety of plants
on a farm, as in agroforestry systems, can also reduce the risk of
total crop failure. Evidence shows that combining several types of
plants provides a type of insurance. If the economic benefit of one
crop is reduced by pest damage or market failure, the farmer can
make up for it by harvesting another crop. Also, growing a variety
of species makes the farm less vulnerable to any one pest.

Income generation and
distribution

Agroforestry practices
can increase farmers' annual income. Some increases in revenue come
from harvesting different tree crops in different seasons. For
example, in many Asian countries farmers use the leaves off
Artocarpus heterophyllus (jackfruit) as fodder during the driest
season. The same trees produce fruits providing income and food to
the owner at other times. The result is that income and employment
are distributed more evenly throughout the year.

Of course there are many
other reasons for growing trees on farms. Trees provide shade for a
cooler soil temperature, reduce loss of soil moisture and also
protect the soil from wind and water erosion.

Selecting appropriate
species

Successfully growing multipurpose trees depends, to a great
extent, on selecting the most appropriate species. To do this,
farmers must first have a clear idea of why they wish to grow
multipurpose trees and which tree crops match the needs of their
particular farming system and local agroecological conditions.

People grow trees for different purposes: to obtain timber, fuelwood,
fodder, or food; to conserve the soil; or a combination of these. Trees
can also be grown in different land use systems, such as alley cropping,
home gardens, farm woodlots, or industrial plantations. These different
purposes and growing systems determine the criteria that farmers must
consider when selecting which species to grow.

Fuelwood

Species grown for this purpose should:

adapt quickly and yield a maximum volume of wood in a short
time;

stabilise the soil and maintain its fertility;

require minimum time and effort for management;

tolerate diseases and pests;

tolerate drought and other climatic stresses;

coppice well, that is readily sprout shoots from stumps;

have other uses that contribute to the farm enterprose;

produce trees without thorns and whose stems and branches have a
diameter small enough to be cut with hand tools and be easily
transported;

Matching species to
requirements

Site characteristics

Multipurpose trees offer many opportunities but do
not guarantee benefits. When selecting a species, it
is important to consider soil conditions, climate
and topography. After deciding on the planting
objective and learning about the soil, rainfall and
other conditions of the planting site, the farmer
can decide whether to grow indigenous or exotic
species.

Indigenous versus exotic
species

Species found growing in
nearby natural stands, or trees growing well in neighbouring
plantations are good choices. Some of these species may be
indigenous, which grow and reproduce naturally in the region. Others
may be exotics, that is, have been introduced from another region or
even another country. For example, Eucalyptus spp were
introduced throughout Asia from Australia.

When introducing an exotic
species it is important to determine whether the soil, rainfall, and
other requirements of the species match the conditions of the
planting site. If the most suitable species are not known and there
are only a few sources of tree seed in the area, indigenous species
as well as local exotic species should be considered first. Local
exotic species are those found in botanic gardens, on farms, in
parks or along roadsides and that have survived under local
agroecological conditions.

Environmental matching

The most
frequently used technique for selecting an exotic
species is called environmental matching. The
technique calls for examining the species in its
home environment or testing its growth in other
countries with environmental conditions similar to
those found in the home environment. Some species
grow well in areas far from their original home if
the new place has the same type of environment. When
ordering seeds from outside the area to be planted,
obtain supplies from more than one source. If one
source performs poorly, there is still a chance that
seed from another source will succeed.

Preferences of end users

Species should
match the preferences and needs of end users. When
farmers grow trees for their own use, they know the
types of tree crops that they wish to obtain. When
farmers grow trees for sale, it is important that
they know the preferences of buyers.

Technical requirements

Some species require
intensive management techniques beyond the means of small-scale
farmers. Such species should be avoided, regardless of potentials
they may appear to have.

Potential competition with
other crops

Introducing an exotic species can result in undesirable
side effects. One possible problem is that the species will adapt so well to its
new environment that it will become a weed and take over crops that are
important to farmers' livelihood. For example,
Prosopis juliflora, native to Central America and the West Indies, was
introduced to India as a fodder and fuelwood tree.

Some scientists say
that it grows so well in its new environment that it inhibits the germination
and growth of other plants that are more valuable to the farmer.

Availability of Planting Material

Seeds or seedlings of the selected species should be readily available.
Availability of planting material can be limited because:

It is difficult to grow seedlings in local nurseries.

It is difficult to establish the seedlings in local plantations.

There are quarantine restrictions on seed coming into the country.

Seeds and seedlings of the species are
susceptible to local diseases and pests.

Suggested Readings

Boland, D.J. 1986. Selection of Species and Provenances for Tree
Introduction. In: J.W.Turnbull, ed. Multipurpose Australian Trees and
Shrubs: Lesser-known Species for Fuelwood and Agroforestry. Canberra,
Australia: ACIAR.